pad a binary string with zeros?

retrotron

I need to pad binary strings with zeros. How do I do that?

Suppose I have '1111' but I need it to be '01111'. How would I do that?

Merve

PHP supports automatic type conversion.

so:
<?php
$num = 1111;
$new_num = "0".$num;
?>

laserlight

Well, there is [man]str_pad/man....

retrotron

The problem is PHP strips all left 0s from binary strings...I think that's what's happening anyways. So even when I add a 0 like Merve had it or with string pad, it still strips the left zeros. E.g. when I do

$num = 1111;
$new_num = '0'.$num;
echo $num;

I still get an output of 1111 instead of 01111 because that leading 0 gets stripped. The same happens with str_pad when the number is converted to a binary string. Does that happen to anyone else?

retrotron

I managed to get pack () to work. Here it is in a function:

function padBinStrLeft ($binStr, $leadingZeros) {
  $bin = $binStr;
  for ($i = 0; $i < $leadingZeros; $i++) $bin = pack ("aa*", 0, $bin);
  return $bin;
} // end padBinStrLeft ()

// pad '1111' with 2 zeros
$binStr = padBinStrLeft (1111, 2);

Merve

How about this:

<?php

$num = 1111;
$new_num = (string) '0'.$num
echo $num;

?>

AstroTeg

Leading 0's on a binary string are considered insignificant digits. Although having leading zeros are handy for output and makes things look pretty. If all you're doing is output, you might try this:

echo sprintf('%08d', $binary);  // 8 digits

echo sprintf('%06d', $binary);  // 6 digits

echo sprintf('%04d', $binary);  // 4 digits

You may find it easier to let [man]sprintf[/man] to handle the padding for you...

retrotron

Yeah, sprintf didn't work for me either, though I'm not sure why. I just tried it again and it still didn't work. With this code:

$num = 1111;
$new_num = sprintf ('%06d', $num);
echo $num;

I get the output 1111. Any idea why it doesn't give me the extra zeros?

Yeah, left zeros don't change the value of binary strings (01111 == 1111), so PHP drops them (probably for speed?), but I need those zeros in this case because I have to string bit strings together and make sure they're aligned. 😉

AstroTeg


$num = 1111;
$new_num = sprintf ('%06d', $num);
echo $num;

This prints out 1111 because you're echoing $num and not $new_num. Try this:

$num = 1111;
$new_num = sprintf ('%06d', $num);
echo $new_num;

retrotron

Ha ha, I'm retarded. I must have been doing that before too. :rolleyes: